A grid of thousands off photodiodes that absorb photons from light and emit electrons

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Where are CCDs found?

Digital cameras, astronomical telescopes and digital X-ray machines

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What does CCD stand for?

Charged coupled devices

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What properties of light does the wave theory explain?

Reflection, refraction and diffraction

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How can the photoelectric effect be demonstrated?

A clean sheet of zinc is placed on a negatively charged gold leaf electroscope. UV light is directed on the leaf and the electroscope discharges. However if the leaf is positively charged it remains charged

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What does the photoelectri effect demonstration prove?

That the UV light kocks electrons off the metal surface and are released as photoelectrons

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What is thermionic emission?

When a strong light source is directed at a heated metal wire the electrons gain enough energy for them to escape the attractiv forces of the wire

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Using wave theory what shoul happen if you shon a bright white light on a metal

After a small delay the light would heat the metal and release electrons

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Define quantum of light

A small indivisble package of energy

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E=hf

E-energy of a photon(J) h-plancks constant(Js) f-frequency of light(Hz)

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What did planck suggest?

That one photon reacts with one electron and the photons energy is absorbed by the eletron

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Define threshold frequency

The minimum frequeny of light required to cause the photoelectric effect

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Defin intensity

the rate of enrgy transfer per unit area

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Define photoelectron

and electon emitted during the photoelectric effect

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If the frequqency is below the threshold frquency what happens?

No photoelectrons are emitted

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What materials can visible lights remove photoelectrons from?

alkali metals, alcium, barium

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What happens if you increasae the intensity of light?

More photoelectrons are emitted(as long as the threshold frequency is met)

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What is the potential well?

A model to help us understand why electrons require energy to remove them from a metal. An electron has its least potential enrgy in the potential well

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What kind of force is in the potential well

Electrostatic attraction

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What does the depth of the well represent

The minimum energy required for electrons to escape a metal

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What requires least energy? Releasing electrons from the surface of the metal or deep in the metal?

Surface

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Define threshold energy

The minimum amount of energy required to cause the photoelectric effect

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As light intesity increases what happens to the photoelectrons?

More are emiited but the energy of each one stays the same

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What is the maximum kinetic energy?

The difference between the threshold energy and the photons energy

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Define work function

The minimum energy needed to release a photoelectron from a material. This is equal to the threshold frequency